I have to say, I certainly would not feel safe knowing that all the 16 year-old, phone gabbin'young ladies in their brand new Mustangs (courtesy of Daddy) and timid, self righteous, couldn't-think-ahead-if-their-Expedition-depended-on-it woman drivers were allowed to go THAT fast. Most of them don't have the attitude or aptitude to drive anything bigger or more powerful than a Civic anyway.
I think there should be a 90-100mph speed limit, sure, but it should only apply to fuel-efficient motorcycles ridden by individuals who actually think about whats going on up ahead, realizing that they'll be there in a few seconds.
The fact is, the majority of motorcyclists are way more focused on what they're doing, and what other drivers are doing. Not only does riding lend itself to more focused, attentive behavior, but motorcycles are really the only practical way of doing 90-100 mph for long distances because most cars and trucks would guzzle fuel terribly.
So how about it? 70 for anything with four wheels, and 100 for bikes? Operator discretion would have to used as far as how fast you can run your bike for extended periods(no 82 GS650s doing 100 for 50 miles straight), but it would present bikes as a much faster, and still cheaper way to commute, or get just about anywhere by freeway.